GT6 fuel tank fittings

[Bruce_the_GT6]

Hi,

Could I ask for some help in trying to identify the fuel pipe union I require.  I have replace the fuel tank on my MkII with an after market replica tank (not going to comment on the agro that has caused), but anyway, I cannot use the old pipe nut / olive set up.  I’m trying to identify the thread size etc so I can order the correct part.  I know I need pipe diameter 5/16”, but not sure on the thread size required - I’m guessing 1/2” and I assume BSPT type - but tbh very confused. Any help would be appreciated before I leave this supposedly replicable car to sit for yet another year.

Thanks 

[Colin Lindsay]

Rimmers state it's a 3/8 thread on a 5/16 pipe, but don't give the actual thread. I'm apt to be lazy in such things and just buy the listed part rather than try to source it from thread etc.

When you say you cannot use the old nut, is this due to incorrect threads, or it just won't reach? Have you tried it for fit? Just thinking out loud...

[Dick Twitchen]

Just measured a spare 3/8 tube nut and it's 20 tpi.  I would support Colin's thoughts on trying to fit the old nut, but begs the question why you "cannot use the old set up" even if replacing with new parts? 

[Bruce_the_GT6]

Thanks for the response. I can’t use the old fitting as alicool tanks have the pipe fitting Does not have anything for the olive to press against. The nut can be tight, but the pipe spins and leaks.

[Colin Lindsay]

That could be a real problem in getting a seal, if there's nothing at all to compress, either olive or flare. The pipe will leak round the nut, as you've found out. What fittings do the makers recommend?

[Bruce_the_GT6]

They didn’t recommend any fittings. They claim it’s an exact replacement. Fitting required cutting a cross bar in the boot, modifying the fuel sender and this pipe problem.

[Colin Lindsay]

So it isn't... an exact replacement, that is. Ask what preferred methods they have for sealing the fuel outlet, given that it will take neither a flare nor an olive - if they have a recommended leak-free system then maybe it can be spliced into a 5/16 fuel line using a flexible joint, such as a short length of rubber hose. If they insist that it takes the original setup, well obviously it doesn't. They can't provide an item that's not fit for purpose, especially one so potentially dangerous as a fuel tank.

Alicool claim that it's "a direct replacement without any alterations and fits original sender unit and fuel pickup". You'll need to make contact and inform them that it doesn't measure up, then see what they'll do.

[Dick Twitchen]

Bruce,

I have an Alicool tank and also had an issue to start with until I found the fitting was for 5/16 and not 1/4 (Mk1); a size difference they were not then aware of.  However, having then changed pipe size I had to try  a couple of different tube nuts before finding one that worked.  A long one with a pronounced neck at the end and a copper olive (Screwfix) worked fine.  Best photo I could find courtesy of Moss.

Dick

https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.moss-europe.co.uk%2Ftube-nut-male-steel-5-16-unf-grp12.html&psig=AOvVaw0wkac8vYRqq2ulpOfwmkV1&ust=1593954669654000&source=images&cd=vfe&ved=0CAIQjRxqFwoTCPCinIHWs-oCFQAAAAAdAAAAABAG